Filtration systems are required for swimming pools, spas and the like to remove solid particles from the water and keep the water clean. In one type of filtration system, a filter cartridge is mounted in a reservoir or recess in the wall of the pool or spa. Water enters the recess from the pool or spa and passes through the filtering element of the filter cartridge and is dumped through an outlet opening in the recess back into the pool.
Conventional filter cartridges used in such systems generally have a cylindrical filter element comprising one or more layers or sheets of a porous material, the pore size of the material determining the minimum size of the solid particles which the filter element will remove. The filter element is typically pleated or corrugated to increase the filtering surface area of the material, and hence, to increase the rate at which fluid can pass through the filter element,
The filter cartridge also comprises a generally rigid, perforated, cylindrical core which extends the length of the cartridge and lines the interior of the filter element. The filter element and core are sealed at their ends to generally rigid annular end caps. The end caps and core give structural integrity to the cartridge.
In one typical arrangement, a perforated pipe which is fitted in the outlet opening and extends upwardly into the recess. The filter cartridge is mounted in the recess in such a manner that the pipe extends through the core of the filter cartridge. A nut is mounted on the end of the pipe which protrudes from the top of the filter cartridge and holds the filter cartridge in place.
In another typical arrangement, a small section of pipe is fitted into the outlet opening so that it protrudes a short distance upwardly into the recess. The diameter of the pipe is about the same as the inner diameter of the lower end cap. The filter cartridge is fitted onto the pipe, with the pipe extending through the end cap and into the core. The filter cartridge is held in place by the snug fit between the pipe and lower end cap. In such an arrangement, the upper end cap is either a solid disk, i.e., no opening. or if an annular disk is used, the opening is plugged.